Method of applying an aluminum coating on ferrous metal article



May 8, 1962 D. K. HANINK ET AL 3,033,705

METHOD 0E APPLYING AN ALUMINUM coATING oN FERRoUs METAL ARTICLE Filed Aug; 13, 1956 M L a TED JZ* l, ,70 TA Z v V L VES 604/ @PAM Ks QQ AL 0MM/0M 0^/ ww. v5 65A r ,c4 ce @Norbey United States Patent O 3,033,705 METHOD OF APPLYING AN ALUMINUM COAT- ING N FERROUS METAL ARTICLE Dean K. Hanink, Indianapolis, Ind., and Albert A. Shoudy, Jr., Royal Oak, Robert F. Thomson, Grosse Pointe Woods, and August G. Mette, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Aug. 13, 1956, Ser. No. 603,536 5 Claims. (Cl. 117-50) This invention relates to the treatment of metal articles and is more particularly concerned with a method of forming an extremely thin, adherent layer of an alloy of aluminum with the base metal of the article whereby the composite structure is resistant to oxidation and corrosion and especially under elevated temperature conditions. The process is especially adapted to process articles such as poppet valves for internal combustion engines, apper valves, ybuttery valves, tube support hangers, spark plug shells, and similar articles.

vWith the advent of high-compression internal combustion engines and the more extensive use of leaded fuels in recent years, valves in such engines have been subject -to rapid oxidation and high-temperature corrosion by the hot combustion gases. Gases resulting from Ithe burning of leaded gasolines are particularly detrimental and greatly shorten the life of valves of internal combustion engines. Consequently, valve failure frequently occurs either because of high-temperature corrosion of the valve seating face or because of corrosion of the stern immediately adjacent the valve head. Severe corrosion of this stem results in itsynecking down to a point where its stem will actually fracture.

To alleviate the aforementioned oxidation and corrosion problem and to considerably increase the life of poppet valves, these valves may kbe coated with aluminum or aluminum base alloys. A suitable process for coating valves with aluminum is disclosed in co-pending patent application Serial No. 574,875, tiled March 29, 1956, in the name of Dean K. Hanink, and now U.S. Patent No. 2,881,750, and in turn is a continuation-in-part of patent application Serial No. 364,673, tiled .l une 29, 1953, now abandoned. This process results in an aluminum coated valve having an extremely thin layer of an alloy of aluminum and the base metal disposed between the aluminum and the base metal of the valve. This layer is provided at the valve seating face and also may be provided around the valve head and neck if desired. Other processes for forming poppet valves with a suitable corrosion resistant layer of an alloy of aluminum with the base metal of the valve are disclosed in copending application Serial No. 459,093, tiled September 29, 1954, in the names of Dean K. Hanink, Albert A. Shoudy, Jr., and Robert F. Thomson, and now U.S. Patent No. 2,885,- 304, assigned to the assignee of the present invention.

The processes described in the aforementioned patent applications have proven highly satisfactory and valves and articles produced thereby have a greatly extended life. However, the aforementioned procedures are somewhat expensive and complicated.

Accordingly, a principal object of this invention is to provide a simple, practical and inexpensive method or process of forming an alloy of aluminum with the base metal of articles such as valves and the like to protect the surface from oxidation and corrosion. Another object of the invention is to provide an improved process of forming a coated poppet valve and the like by a process which is adapted to be rapidly and inexpensively 3,033,705 Patented May 8, 1962 ICC carried out in commercial operation. A further object of the invention is to provide a simple, practical and inexpensive method of forming a poppet valve or other articles in which an extremely thin alloy layer of controlled thickness of aluminum with the base metal of the valve is formed by a diffusion process and wherein it is not necessary to use fluxes or protective atmospheres in order to obtain the desired diffusion layer.

Other objects and advantages of the present invention will become more apparent from a consideration of the following description of preferred embodiments of the invention.

The invention will be described in connection with the formation of thin alloy layers of aluminum on poppet valves for internal combustionvengines although it will be understood that the principles of the invention have application 'also to other articles.

The process broadly comprises preheating t-he valve, metalizing the valve with aluminum and thereafter heating the metalized valve by high-frequency induction heating to cause aluminum to diuse into the valve an extremely small distance inwardly from the surface. Optimum results are obtained when the preheating also is carried out by high-frequency induction heating means.

In processing the valves, they may be machined and ground substantially to final dimensions. Thereafter, the valves may be cleaned in any desired manner prior to the metalizing operation. A typical cleaning operation comprises degreasing the valves by a conventional degreasing process employing chlorinated solvents. Other satisfactory methods of cleaning comprise treating the articles in a molten electrolytic caustic salt (such as the com- -mercially available product called Kolene) at a temperature of approximately 900 F. The valves then may be washed in water and thereafter preferably further cleaned by acid pickling. An example of a suitable acid pickling bath is an aqueous solution containing about 2% hydroiluoric acid, 7% sulfuric acid, and 10% nitric acid. Mechanical cleaning methods such as grit blasting, sand blasting, etc., may be employed in some cases where it is desired to supplement chemical treatment.

After the valves have been cleaned, the valves are preheated; optimum results being obtained by highfrequency induction heating. The preheating temperature is dependent to some extent upon the type of material being treated. Typical temperatures employed for the preheating may range from about 200-600 F. Usually temperatures of about 350-450 F. are used. Optimum results in commercial operations are obtained when the preheating is carried out by induction heating While the valves are rotating. A typical speed of rotation during preheating for optimum results ranges from 400-600 r.p.m. in most instances. However, speeds both higher and lower than this may be employed. After the valves have been preheated, the valve seating face has molten aluminum sprayed thereon by means of a metalizing gun of conventional type; lfor example, an oxyacetylene metalizing gun. Aluminum wire is fed to the metalizing gun at a desired rate such that a substantially uniform amount of aluminum is applied to each valve at the valve seating face thereof. For typical automotive valves, 0.050 to 0.085 gram of aluminum per valve provide satisfactory results. By rotating the valve during application of the molten aluminum by the metalizing gun, the metalized coating is deposited in a uniform layer at the valve seating portion.

After the valve seating faces have been coated with aluminum,

uniformly the valves and coating are then heated by high-frequency induction to cause the aluminum to diuse into the valve seating portion of the valve. Optimum results in commercial production are obtained by rotating the valves during the diiiusion treatment. Typical temperatures to which the seating face of the valve and coating thereon are heated by induction to cause the desired diffusion may range from approximately 1425-1625 F. Typical heating times at these temperatures may range from about 16 to about 20 seconds. After the diffusion treatment, the valves are cooled to room temperature.

The alloy layer or diffusion zone of the aluminum with the base metal of the valve must, in all cases, be extremely thin in order to prevent spalling or aking of the protective layer. In general, the thickness of the alloy layer of the aluminum with the base metal of the valve will be within the range of from 0.00005" to 0.0015" and the aluminum will have a thickness usually not more than 0.004". A very satisfactory alloy layer is one having a thickness within the range of 0.0002 to 0.0011. in some applications, it is of some advantage to have a minimum thickness of the alloy layer of 0.0005. The amount of aluminum applied and the time and temperature of the induction heating are controlled to provide the necessary thin alloy layer.

The sprayed coating material may be eitheraluminum or an aluminum base alloy. By aluminum base alloy is meant an alloy of aluminum which contains about 80% or more of aluminum. Where the word aluminum is referred to in the claims to refer'ito the sprayed material, it is intended to include not only pure aluminum or commercially pure aluminum but also the aluminum base alloy containing about 80% or more of aluminum.

The process readily lends itself to fast, economical commercial production. The induction means for preheating and for diffusing may simply consist of baretype induction heaters. A portion of the bar-type induction coil may be disposed on each side of the valve stem immediately underneath the head of the valve and another portion over the head of the valve. Conveyor means may carry the valves past the heating means with the stem between the side portions and the head underneath the overhead portion of the bar-type coil. In one typical commercial'application of the invention, the valves are moved in a line past the preheating means tto a station where the valve seating faces are sprayed with aluminum from a metalizing gun and thereafter are moved through the induction heating means for causing the diiusion of aluminum into the valve seating face. The valves are rotated about their axes as they move in the line past the two heating means and the metalizing gun disposed therebetween. Typical speeds of rotation are on the order of 40G-600 rpm. It will be understood that normally the valve is rotated several times on its axis during the time that it is within the induction heating means and while it is being sprayed with aluminum.

By means of the high-frequency induction heating means, the appropriate portions of the valve head are rapidly heated to the desired temperatures. By employing high-frequency induction heating means, the metal of the valve is heated rapidly from the inside out, such that there is little chance for the aluminum and valve material to become oxidized and thereby prevent, or detrimentally affect, the ditusion of aluminum into the base metal of the valve at the valve seating face. Thus, fluxes and/ or protective atmospheres are unnecessary. Heating by meansof the induced high-frequency current causes the sprayed'aluminum to melt and diffuse into or alloy with the base metal of the valve for a short distance from the Vsurface to a Vdepth within the range of 0.00005 to 0.0015".

The induction heating means may employ high-frequency cycles similar to those used heretofore in heating other articles by induction means. Very satisfactory re suits have been obtained with cycles of 9600 per second.

The cycles may range as high as 450,000 per second, or even higher. Frequencies somewhat lower than 9600 per second also may be used for particular applications, and induction heating methods employing such frequencies are also considered herein as high-frequency induction heating.

With a certain automative valve, about 0.05 to 0.08 gram of aluminum is deposited on the valve seating face. With this particular automotive valve, a time of about 17 seconds within the induction heating coils provides a diffusion temperature of about 1400 F. With certain exhaust valves, diiusion temperatures of 14001650 F. have proven satisfactory.

The base metal of which the valve is formed may be of any suitable valve material. Typical and illustrative examples of valve materials are the following:

Example 1 Percent Carbon 0.80 Manganese 0.40 Silicon 2.25 Chromium 20.00 Nickel 1.30 Balance substantially all iron.

Example 2 Carbon 0.45 Manganese 1.00 Silicon (max.) 1.00 Chromium 23.75 Nickel 4.75 Molybdenum 2.75 Balance substantially all iron.

Example 3 Carbon 0.45 Manganese 0.40 Silicon 3.125 Chromium 8.50 Balance iron.

Example 4 Carbon 0.20 Manganese 1.40 Silicon 0.80 Chromium 21.00 Nickel 12.00 Balance iron.

Example 5 Carbon 0.45 Manganese (max.) 0.70 Silicon 0.55 Chromium 14.00 Nickel 14.00 Molybdenum 0.35 Tungsten 2.50 Balance iron.

Example 6 Carbon 0.40 Manganese 1.00 Silicon 3.00 Chromium 19.00 Nickel 8.00 Balance iron.

Example 7 Carbon 0.04 Manganese 0.50 silicon '0.40 Columbium 1.00 Aluminum 0.70 Iron V l 7.00 Chromium A15.00

Balance nickel.

Balance cobalt.

Reference is herewith made to the accompanying drawing, in which:

FIGURE 1 is a view partially in section of a poppet valve having a coating on the valve seating face portion of the valve, the valve being in closed position on the valve sea-t.

FIGURE 2 is a line drawing of a photomicrograph showing the ferrous base metal of the valve, a layer of an alloy or diffusion of aluminum with the base metal of the valve, and a layer of aluminum on the alloy layer.

FIGURE 3 is a diagrammatic view illustrating one form of apparatus for carrying out the process.

FIGURE 4 is a sectional View taken on line 4--4 in FIGURE 3.

In FIGURE 1 there is shown a poppet valve indicated generally by and having a stem 12 and head 14. The valve -is shown in closed position on a Valve seat 16. At the -valve seating face there is illustrated at 18 an alloy layer or diffusion of aluminum with the base metal of the valve. Outwardly from the alloy layer is a thin layer of aluminum 20. The thicknesses of the alloy layer and aluminum are exaggerated in FIGURE 1. In FIGURE 2 the portion designated base metal represents the metallographic structure of the base metal of the valve, while the alloy layer 18 is termed alloy of aluminum and the overlying layer of aluminum 20 is termed aluminum-i.

In FIGURE 3, 30 indicates generally a high-frequency induction preheater, While 32 indicates generally a highfrequency induction heater for diffusing sprayed aluminum into the valve seating face. 35 indicates a metalizing gun of conventional design for melting an aluminum wire 36 and spraying the same onto the valve seating face portion of the valve. Number gage aluminum wire is a typical size. It will be understood that the uncoated valves 10 are loaded into the machine at the left-hand end in FIGURE 3 and are continuously rotated while they are conveyed past the induction preheater 30, the metalizing gun 35, and the high-frequency induction means for heating the valves for causing the aluminum to diffuse therein. After cooling, the valves are unloaded at the right-hand end of the machine.

The high-frequency induction preheater 30 comprises a bar-type induction coil having a portion 34 abovey the heads of the valves and two elements 37 below the head of the valve on each side of the valve stem. The highfrequency induction heating means 3-2 for causing the sprayed aluminum to melt and diffuse into the surface of the valve comprises a bar-type induction coil having a portion 40 above the heads of the valves and two other elements 42 on each side of the valve stem. It will be understood that the portions 34 and 37 are so connected by means not shown that high-frequency induced current is caused to flow between these members. The same applies to elements 40 and 42.

It will be understood that at any particular point in the cycle, the upper bar 34 or 40 may be regarded as positive and the two lower sets of bars 40 and 4Z, respectively, as negative. At the next instant, the two lowerbar members of each set may be regarded as positive and the upper bar member as negative. By arranging the bar-type induction heating coils as described, the valves may be continuously rotated as they pass through the machine. The speed of the conveyer is a function of power input and coil length.

It is, of course., not necessary to rotate the valves if other forms of apparatus are employed. Induction heaters having coils surrounding the valve seating face may be employed, if desired. However, the system illustrated in FIGURE 3 lends itself to mass production techniques.

While this invention has been `described by reference to certain preferred embodiments and conditions, it will be understood that the invention is not limited thereby and numerous changes and modifications will be apparent to those skilled in the art Without departing from the spirit and principles of the invention.

We claim:

1. A method of forming a ferrous metal poppet valve characterized by its resistance to oxidation and corrosion under high-temperature conditions, which comprises rotating a valve while it is being preheated by induction to a temperature of 200 to 600 F., thereafter spraying a thin coating of molten aluminum onto the heated valve seating face of the valve while it is rotating to provide a thin uniform layer of aluminum thereon, and thereafter induction heating the valve while lit is rotating to a temperature of about 14001650 F. for a time Within the range of about 16-20 seconds, thereby diffusing or alloying aluminum with the base metal of the valve to a depth within the range of 0.00005 to 0.0015.

2. A method of forming a ferrous metal valve characterized by its resistance to oxidation and corrosion under high temperature conditions, which comprises rotating a valve at a speed of about 400 to 600 rpm. while it is being preheated by high frequency induction to a temperature within the range of 200 F. to 600 F., thereafter spraying molten aluminum onto the heated seating face of the valve while it is rotating at said speed to provide a thin uniform layer of aluminum thereon, and thereafter diffusing said layer of aluminum into the said valve seating face to a depth Within the range of 0.00005 inch to 0.0015 inch by induction heating the valve face to a ternperature of about l400 F. to 1650 F. for only a time suicient to cause said diffusion while it is rotating at said speed.

'3. A method of forming a ferrous metal valve characterized by its resistance to oxidation and corrosion under high temperature conditions which comprises rotating the valve, preheating the rotated valve to a temperature within the range of about 200 F. to 600 F., thereafter spraying molten aluminum onto the seating face of the heated valve while it is rotating to provide a thin uniform layer of aluminum thereon, thereafter diffusing said aluminum into the valve seating face to a depth within the range of 0.00005 inch to 0.0015 inch by induction heating the valve to a temperature of about 1400 F. to 1650 F. for only a time suicient to cause said diffusion while it is rotating.

4. The method of forming a high temperature oxidation and corrosion-resistant ferrous metal valve article which comprises -preheating to a temperature of 200 F. to 600 F. by high frequency induction at least a portion of the article, spraying molten aluminum onto the said preheated portion while rotating said article to provide a thin uniform layer of aluminum on said portion, and thereafter diffusing the sprayed aluminum to a depth within the range of 0.00005 inch to 0.0015 inch by induction heating said portion at a temperature and for only a time sufficient to cause said diffusion.

5. A method of forming a ferrous metal article characterized by its resistance to oxidation and corrosion under high temperature conditions which comprises rotating the article at a speed of about 400 to 600 r.p.m. while it is being preheated by high frequency induction to a temperature within the range of 200 F. to 600 F., thereafter spraying molten aluminum onto the preheated article while it is rotating at said speed, and thereafter diffusing said aluminum into the said article to a depth within the range of 0.00005 inch to 0.0015 inch by induction heating said article to a temperature of about 1400* F. to 1650 F. for

7 8 only Aa time sucient to cause said diffusion while it is 2,744,032 Highfield May 1, 1956 rotating at said speed. 2,757,445 Anger Aug. 7, 1956 References Cited in the le of this ptent Iglor'l''t-glf'n" ylg" UNITED STATES PATENTS V Y 2,361,962 Ronay Nov. 7, 1944 *FOREIGN PATENTS v v 2,422,417 Hutchinson June 17, 1947 577,427 Great vBritain May 17, 1946 2,544,671 Grange et al Mar. 13, 1951 620,165 Great Britain Mar. 21, 1949 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,033,705

It is hereby certified that error appears in the above numbered pat- May 8, 1962 Dean K. Hanink et al.

ent requiring correction and that the said Letters Patent should read as corrected below.

Column 5,

Signed and SEAL) Attest:

EsToN G. JOHNSON SRNEXRMXMXIERX Attesting Officer line 67, for the numeral "40" read 37 sealed this 27th day of November` 1962.

DAVID L. LADD Commissioner of Patents 

4. THE METHOD OF FORMING A HIGH TEMPERATURE OXIDATION AND CORROSION-RESISTANT FERROUS METAL VALVE ARTICLE WHICH COMPRISES PREHEATING TO A TEMPERATURE OF 200*F. TO 600* F. BY HIGH FREQUENCY INDUCTION AT LEAST A PORTION OF THE ARTICLE, SPRAYING MOLTEN ALUMINUM ONTO THE SAID PREHEATED PORTION WHILE ROTATING SAID ARTICLES TO PROVIDE A THIN UNIFORM LAYER OF ALUMINUM AN SAID PORTION, AND THEREAFTER DIFFUSING THE SPRAYED ALUMINUM TO A DEPTH WITHIN THE RANGE OF 0.00005 INCH TO 0.0015 INCH BY INDUCTION HEATING SAID PORTION AT A TEMPERATURE AND FOR ONLY A TIME SUFFICIENT TO CAUSE SAID DIFFUSION. 